Just ordered this engine 
(I have to do something when on holiday being baked by the sun )
It’s an ULPower UL350i and it’s going to sit on the nose of my Onex. It will be a real blast. 120 HP, FADEC and and a single seater with MTOW 470 kg (as opposed to 70 lazy VW originally). Fully aerobatic as well.
Not cheap, about €25k in total, but I need the power where I fly, and I need to be sure the engine is running. Thus, the main reason to buy it. I just couldn’t get the confidence I need to fly it with the Aerovee (VW conversion).
Look here for specs etc.
Nice. Please keep updates, I might need a new light engine sometime, too. At the moment I have an O235 mounted.
What speed are you planning on running the UL engine and propeller? One of the things I’ve understood about the UL engines is that peak power is rated at above the rpm that most owners are actually running them, for reasons not clear, and that owners are therefore getting about 90% of rated power. Any thoughts?
The above comes largely from a propeller manufacturer friend who supplies variable pitch and ground adjustable propellers for a wide range of engines.
Having been in an airplane when the VW engine failed (followed by a ride to the ground) I agree about those engines. It would take a convincing argument to get me in the air behind one again. Is the weight of the UL and prop significantly higher than the VW in relation to the W&B requirement for your plane?
Silvaire wrote:
One of the things I’ve understood about the UL engines is that peak power is rated at above the rpm that most owners are actually running them, and that owners are therefore getting about 90% of rating power. Any thoughts?
This is what UL posts on their homepage:
Rated power should be sufficient for any VW-conversion exchange.
The efficiency sweet spot seems to be in an acceptabe rpm-range, too.
Quite similar to the L2400, just some 10-15 kg lighter: http://limflug.de/downloads/datasheets/L2400-DT_ET-datasheet-en.pdf
And 30-40 kg lighter than my O235 with inverted fuel, oil and shitty accessible magnetos…
@LeSving do you know more about aerobatic capabilities? The manual of the UL350i only mentions 3 seconds up to -0,5g – that is a bit low on the aerobatic side. Or is there an unlimited aerobatic option?
The power curve fits what I’d heard, peak power at 3300 rpm. For reasons unknown to me, owners are very often running them with lower peak rpm, more like 2800. This obviously could have something to do with propeller efficiency calculations for the best overall package, that depends on a myriad of propeller design trade-offs. Regardless the result is an engine that makes about 10% less power in service than the dyno would indicate. There is also this from the Operating Manual, which is ambiguous as to maximum recommended climb power rpm.
General operating limits
Max. engine speed …………………. 3300 rpm
Recommended prop speed ………… 2200 – 2800 rpm
VWs running at similar propeller rpm have suffered low propeller efficiency for decades and obviously Rotax had this very much in mind when gearing the output shaft on the Rotax 912 in the ‘80s. The other solution (instead of rpm) is more displacement/torque which then leads to six cylinders or larger cylinders + higher quality fuel being required. There’s never been a free lunch.
A practical issue is hydraulic valves or not. For a VW replacement this would be a big selling feature as constant valve adjustments and propeller re-torques are a typical part of the VW aero-engine experience. The UL has non-hydraulic valves and requires valve adjustment every 50 hours of operation after more frequent checks during break-in after any cylinder head work. Most VW owners would do valve adjustments about twice as often. Most aircraft engines (although not all) require no valve adjustments.
The 350 when installed, fully equipped, weigh almost exactly the same as the Aerovee (also fully equipped). The CG will be the same. The 260 is a bit lighter, but not much, 4-5 kg I think, or less.
The 350i is not aerobatic (I meant the airplane ). The engine can only handle 3 seconds of negative g. I only plan positive g flying (nice gentleman’s aerobatics). the 350iSA is fully inverted and can do unlimited negative g, and it has more HP (130).
The 350 is a longer stroke 260. That’s the only difference between them. But the difference in stroke is huge though. As I understand it, the 350 is better fitted for direct drive and fixed pitch in the sense that the peak torque is at a lower rpm (more in the sense that the torque drops more sharply from peak rpm to be more precise). It’s probably easier to make a good fixed pitch prop for a 350 than for a 260?
I don’t think rpm as such has much to do with efficiency, it’s relative speed of the blades that matters. More rpm requires smaller diameter to be efficient, but at a higher IAS. Smaller diameter produces less static thrust and so on. A Rotax with the gear and low propeller rpm will be more efficient overall I guess, because you can use a larger diameter prop and achieve equal efficiency (and thrust) at high speed but at the same time have more static thrust. The price for that is the gear (more complexity).
With the 350i I have so much surplus power that it doesn’t matter. More than enough static thrust and loads of power in level flight. The Onex is designed to fly just fine with 70-80 (theoretical) horse power. It becomes very much like an RV with a high enough power to weight ratio to make discussions almost purely academic. A 912iS with CS prop would probably be better, but maybe not, because the prop diameter is restricted by the airframe/landing gear. This would mean more blades and less efficiency. Besides, no one is making engine mounts for the Rotax, so it’s a moot point at this time. With a CS prop, the main important factor is hp anyway, regardless of how that hp is obtained.
The rpm is electronically restricted to 3300. It has 116 HP at 2800 rpm and 120 at 3300. At 2800 you “lose” 3% of max theoretical power. The iS/iSA has 123 and 130 at those rpms.
The 260 has 85 hp at 2800 rpm and 97 at 3300, thus “lose” 14 % while the 260 iS/ISA has 93 and 107 (15% “lost”). I think the difference with the 350 is the much longer stroke, The stroke is increased from 74 to 100 mm.
Do you, by chance, know the price for the 350iSA?
No, it’s probably not all that more expensive, but I really don’t know. If you contact ULPower, they will answer right away though. Included in the price is also a two day course at the factory and everything needed to run the engine (coolers, fittings, piping, tubes sensors etc even baffling) + the tools, oil and stuff for the first maintenance. “Free” shipping to my home in Norway also There could be differences for Germany.
You have a choice of single or double ECU. The ECU communicates via CAN bus and/or RS232 to your EFIS or whatever engine instruments you have. This includes RPM, fuel flow, oil temp, air temp, throttle position, fuel pressure, oil pressure, ECU temp, battery V, atmospheric pressure and check lights. The only thing that is not via CAN is separate EGT, CHT and MAP.
LeSving wrote:
The rpm is electronically restricted to 3300. It has 116 HP at 2800 rpm and 120 at 3300. At 2800 you “lose” 3% of max theoretical power. The iS/iSA has 123 and 130 at those rpms. The 260 has 85 hp at 2800 rpm and 97 at 3300, thus “lose” 14 % while the 260 iS/ISA has 93 and 107 (15% “lost”). I think the difference with the 350 is the much longer stroke, The stroke is increased from 74 to 100 mm.
Thanks for that, it looks to me like you selected the better model as long as the massive 1 inch stroke increase over the 260 hasn’t hurt reliability. It’s roughly ‘square’ at 105.6 × 100 mm bore and stroke so it should be OK. With direct drive aircraft engines more displacement is generally a good thing as long as weight is controlled and the bore size (indirectly meaning fuel octane requirement) isn’t too large. The UL350 needs 93 AKI (R+M/2) octane fuel which is not available for example in most areas of the US, although 100LL would work there, so its on the edge of what can be done with car gasoline.
The comparison of the different ULPower models reminds me of the same comparison 80 years ago on similar engines, designed for similar applications: the 2300 rpm A-65 (O-170) Continental sold zillions of units while the 2550 rpm Lycoming O-145 was a failure at the same rated power output. The torque on the O-145 dropped off faster resulting in a steeper power curve, exactly as you’ve described when comparing the UL Power engines. Either then or now the smaller displacement engine makes a lot less power at realistically reduced propeller rpm, and power also continues to drop off faster with further rpm reductions, meaning the plane won’t climb well with a fixed pitch propeller and reduced engine rpm at climb speed. Manufacturer quoted peak power is not necessarily the main issue.
The ULPower 350 has about 200 cc more displacement than a 100 HP O-200 Continental, and has specific power in a reasonable range (116 HP) for a flat power curve below the real world 2800 maximum rpm, where the higher power in comparison to the O-200 comes from more displacement and an increased compression ratio (8.7 versus 7:1) that’s possible as a result of higher minimum octane fuel (i.e. not 80/87). You can spin an O-200 to over 4000 rpm if you want to play the same game with high rpm, as done as standard practice on Reno racers… but their high rpm propellers aren’t ideal either. At the other extreme, in combination with the 1930s low rpm light aircraft engines the large 74 inch diameter propellers were good, lots of blade length in relation to root effects, but they had to be because the engines weren’t making much power (or burning much fuel).
I think valve adjustments at 50 hr intervals is the next thing ULPower should address now they’ve controlled weight and added enough torque – valve adjustments haven’t been necessary on other engines for over 80 years. A little bit lower compression ratio (8:1?) would also add practicality for markets where auto fuel octane is limited by environmental regulations.
Silvaire wrote:
The UL350 needs 93 AKI
No. There are two version of all ULPower engines. A “low compression” and a “high compression”. Thy are designated “i” and “iS” respectively. I have the low compression version deliberately to be able to fill any fuel available (Mogas 95 in my case). The “i” needs minimum AKI 91 (or Mogas 95) while the “iS” needs minimum AKI 94 (or Mogas 98, ie “super” as we call it). They will all run just fine with UL91 or 100LL, but using 100LL you need more frequent oil changes. Up to 15% ethanol is OK with all of them.
Manual valve adjustment is per design, deliberately so. Their philosophy is that checking is easy (every 50 hr), and keeping track of this is essential for monitoring faults in the valve train. You can read about it here.
The very basic idea of the ULPower is to make a modern air cooled aero engine. From what I gather, modern means high power to weight ratio, precision manufacturing, FADEC, but also easy to use and easy to maintain and long lasting. Modern does not necessarily mean to include all the newest tech and gadgets. There is no lambda sonde for instance. But I mean, all engines are trade offs between this and that. ULPower offers this particular package. Rotax another one, LyCo a third and so on. This leaves us with several choices, and larger probability to get exactly what we want/need.
